The present invention relates to a structural body made of hollow-shaped material and a method of manufacturing the same. For example, the present invention is preferably applied to manufacturing of structural bodies formed from hollow extruded materials made of aluminum alloy which are used in a railway car, a building structure, and the like.
A friction stir welding method is a technique using a round shaft (called a rotary tool) being inserted into the welding region of members and moving the rotating rotary tool along the joint line, thereby heating, mobilizing, fluidizing and plasticising the welding region, and realizing a solid-phase welding of the members. The rotary tool is comprised of a small-diameter portion to be inserted into the welding region, and a large-diameter portion positioned at the outer side thereof. The small-diameter portion and the large-diameter portion are coaxial. The boundary between the small-diameter portion and the large-diameter portion is slightly inserted into the welding region. This technique is disclosed in Japanese Patent Laid-Open No. H9-309164 (EP0797043A2).
FIG. 9 of the literature discloses welding two faces of the hollow extruded materials from one side. Also, the same discloses a joint which prevents deformation of the hollow-shaped material.
The case where a hollow-shaped material is friction stir welded from one side, as is disclosed in FIG. 9 of the above-mentioned Japanese Patent Laid-Open No. H9-309164 (EP0797043A2) will be considered. In such case, the interval between the upper plates 33, 33 of the two hollow-shaped materials 31, 32 (that is, the interval between the concave portions 39, 39), and the accuracy of the width of the joint 60 being arranged to the region are important. If the interval between the upper plates 33, 33 is smaller than the width of the joint 60, then the joint 60 cannot be arranged thereto. On the other hand, if the interval between the upper plates 33, 33 is larger than the width of the joint 60, it is difficult to perform friction stir welding. That is, it is important to maintain the gap in the butted region between the plate 33 and the joint 60 small.
However, there tends to be formed a large gap in the butted region due to the manufacturing tolerance in the extrusion of hollow-shaped materials 31, 32 or the joint 60. This becomes noticeable in the case where many hollow-shaped materials are juxtaposed and welded, as is in the case of welding a car body of a railway car.
On the other hand, welding the joint 60 to the concave portion 39 by lap joint is possible. By doing so, the interval between the concave portions 39, 39 (interval between the plates 33, 33) could be formed sufficiently larger than the joint 60, and the materials 31, 32 could be manufactured with ease.
However, in such case, the material bends at the connecting region between the plate 33 and the concave portion 39. Therefore, stress concentrates at this region, and the generated stress is increased. Moreover, friction stir welding is performed at the vicinity of the flexure, so that the strength is deteriorated due to the heat effect generated by the welding. As a result of the synergy of these strength deteriorating factors, the allowable stress is greatly deteriorated.
The object of the present invention is to enable welding of the hollow-shaped material from one side, regardless of the size accuracy of the hollow-shaped material and the like.
The second object of the present invention is to enable positioning of the lap joint with ease.
The above-mentioned objects could be achieved by a method of friction stir welding a structural body, the method comprising:
preparing two hollow-shaped materials, each hollow-shaped material including two face plates which are connected by a plurality of ribs, and an end portion of one of the face plates being further projected than an end portion of the other face plate, in which each face plate at the external side of the hollow-shaped materials is substantially flat;
welding the projected face plates together from the other face plate side with friction stir welding;
overlapping a connecting material which is substantially parallel to the projected one of face plates to an end portion of each other face plate of the hollow-shaped materials, in which the position of said connecting material relative to the hollow-shaped materials is determined by a convex portion provided either to the connecting material or to the other face plate during the overlapping; and
friction stir welding said overlap from the external side of the hollow-shaped material.
The second object mentioned above could be achieved by a method of friction stir welding a structural body, comprising:
overlapping an end portion of a first member on top of an end portion of a second member, the position of the first member relative to the second member being determined by a convex portion provided to the first member or the second member during the overlapping; and
friction stir welding the overlap.